Effects of extrinsic electric current on the cyprinid fish EIRG (S-potential).

There have been many discussions on the origin of a sustained negative action potential evoked by illumination within the fish retina, which is known as Svaetichin's "cone action potential" (9) and also as "fish EIRG" ( intraretinal action potential) circumspectively termed by Tomita (10). Recently trials have been made to clarify the accurate allocation of microelectrode tip, making a visible mark inside the retina with various techniques (5, 7, 8, 12). Their results, though being slightly different in detailed points, show that there is no disagreement with the view of Tomita and his colleagues that the characteristic action potential does not originate in the receptor cells but in a proximal layer to the receptors ( 10, 11, 12, 13). It has, however, to be pointed out that, although the activities of bipolar and/or horizontal cells instead of receptors are simply assigned to generation of this negative action potential ( S-potential), it remains still in obscurity whether it is of intraor extracellular nature. As was discussed in a previous paper, it appears to be evident that, even if it is of extracellular nature, the recording must be made from within some kind of compartments isolated electrically from each other (11). The present paper will deal with some electric properties of the cell or the very compartment which gives S-potential in response to light, especially with effective resistance as revealed by passing extrinsic electric current through the micropipette placed inside them.